The invention relates to an optical disc device and a data reproduction method for the optical disc device. Particularly, the present invention is suited for use in an optical disc device for reproducing data which is recorded in an optical disc (multilayered optical disc) having multiple recording layers.
Recently, the storage capacity of a standardized optical disc has been improved by a so-called Multilayered Structure in which a plurality of recording layers are pasted together. For example, a multilayered Blu-ray disc having three or four layers have twice to 2.6 times as large storage capacity as that of a conventional Blu-ray having two layers.
Light sensitivity of each recording layer in a disc including a plurality of recording layers varies depending on differences in materials and structures. Therefore, data in each recording layer is reproduced with optimum reproduction power. If the light is collected on a recording layer with high light sensitivity using reproduction power for a recording layer with low light sensitivity, there is a possibility that the physical state of that recording layer may change and the recorded data may be destroyed due to the difference in the light sensitivity of the recording layers.
Even if a favorable reproduction condition is set to each layer in the conventional optical disc device, once servo deviation occurs, there is a possibility that a focal point may move to another recording layer which is different from a recording layer where the focal point is located, and data recorded in that other recording layer may be deleted unintentionally. As a countermeasure for that problem, the conventional optical disc device adopts a configuration that prevents data deletion by changing, for example, spherical aberration and reproduction power when the aforementioned servo deviation occurs (See Japanese Published Application No. 2008-299982).